Numerical study for predicting tensile damage progress in CFRP laminates with initial fiber cracks

This study investigates the damage progress in CFRP cross-ply laminates with initial fiber cracks, introduced in the fabrication process of composite structures by the use of chopped strands or cutting preforms. The fiber cracks will induce complex damage process and also become the source of the final fracture. Tensile tests were conducted for the coupon specimens with fiber cracks, and the damage progress in these specimens was observed by the soft X-ray radiography. We then evaluated the damage process in the laminate with fiber cracks by the layer-wise finite-element model with cohesive elements. The simulated damage patterns included the matrix cracks along the initial fiber cracks, splits in the 0° layer extending from the tips of the fiber cracks, and transverse cracks in the 90° layer. Delamination was also generated at the crossing point of ply cracks due to the large shear stress, and then extended in the triangular region bounded by the fiber cracks and splits. Furthermore, the damage state at the final failure was obtained in the damage analysis by applying a conventional damage criterion to the fiber breakages. The predicted damage extension to the final failure agreed with the observations. The numerical results also demonstrated that the damage near the initial fiber cracks produced a similar stress field to a penetrating notch.